FURTHER STUDIES ON GYMNOSPERMS. 



215 



developed entirely inside of the macrosporangium, and derives 

 the nutriment for its growth from the cycas plant, which is the 



Fig. 279. 

 Macrosporangium of Cycas revoluta. 



Fig. 280. 

 Roentgen photograph of same, show- 

 ing female prothallium. 



sporophyte. Archegonia are developed in this internal mass of 

 cells. This aids us in deter- 

 mining that it is the prothal- 

 lium. In cycas it is also called 

 endosperm, just as in the 

 pines. 



430. If we cut open one of the 

 mature ovules, we can see the en- 

 dosperm (prothallium) as a whitish 

 mass of tissue. Immediately sur- 

 rounding it at maturity is a thin, 

 papery tissue, the remains of the 

 nucellus (macrosporangium), and 

 outside of this are the coats of the 

 ovule, an outer fleshy one and an 

 inner stony one. 



431. Microspores, or pollen, of 



cycas. — The cycas plant illustrated 



in the frontispiece is a female plant. 



Male pla'nts also exist which have 



... ... ,, , , groups on the under side, b, group of sporangia ; 



small leaves in the center that bear c , pen sporangia. (From Warming.; 



Fig. 2S1. 

 A sporophyll Istamen) of cycas ; sporangia : 



